Selective hydrogenation of acetylenes in the presence of olefinic gases containing unsaturated c4 hydrocarbons



Oct. 3, 1961 H w. FLEMING ETAL 3,003,008

SELECTIVE HYbROGENATION OF ACETYLENES IN THE PRESENCE OF OLEFINIC GASESCONTAINING UNSATURATED C HYDRO'CARBONS. Filed 006. 13, 1958 2Sheets-Sheet 1 RAW GAS AROMA'HC DISTlLLAT E REMOVAL. 4-

fiYDROGENATION" ACID GAS REMOVAL LOW TEMPERATURE H; AND cm' AQSORBER OUTFRAcTmNAToR FRACTIONATORAS HIGH PuRn'Y gm INVENTORS HAM FLEMING F7 1 BYw.n. eu'mmg PRIOR ART Wan Z m Filed Oct. 13, 1958 Oct. 3, 1961 l H. w.FLEMING ETAL SELECTIVE HYDROGENATION OF ACETYLENES IN THE PRESENCE OFOLEFINIC GASES CONTAINING RAW GAS UNSATURATED C HYDR0CARB0NS 2Sheets-Sheet 2 AROMATIC DIST\LLATE REMOVAL COMPRESSION 7 HYDROGENATIONHEAVY OUT AC\D GAS REMOVAL DRYING Low TEMPERATURE AasoRaER H; AND CH OUTFRACTIONATOR FRAcTwNATOR :4 HYDROGENATION HIGH PURITY Cgl'h.

l8 c s'rRIPPER" 0 OUT 3,0 03 SELECTIVE HYDRQGENATION OFiACETYLENES INTHE PRESENCE OF OLEFINIC GASES CON- TAINHNG UNSATURATED C HYDROCARBONSHarold W. Fleming and William R. Gutmann, Louisville,

f Ky., assignors to Catalysts and Chemicals Ino, Louisville, Ky, acorporation of Delaware Filed Oct. 13, 1958, Ser. No. 766,761

4 Claims. (Cl. 260-677) This invention concerns a process" for treatingmixtures comprising olefins and containing substantial proportions ofunsaturated C hydrocarbons and one or more other hydrocarbons with anacetylenic group. it pertains especially to the treatment of mixturescomprising short chain olefins and conjugated diolefins in which it isdesired to remove the more highly unsaturatedimpurities.

Olefins are produced in dilute form but in large quantities in variousprocesses by the pyrolysis of petroleum fractions and other hydrocarbonstarting'materials. The

olefin containing mixtures obtained in such processes .usualiy comprisea variety of hydrocarbons other than "olefins and separation of thelatter in a 'form suitable for use, such as in the production ofpolyethylene, has proven "difi'icult. For instance, cracked butanes,cracked oil gas, or refinery gas, which are well-known sources ofolefins, usually contain parafiinic hydrocarbons ranging tram methane tohexane, olefins such as ethylene, fpropylene, butylene, amylene andhexenes, diolefins'such as propa- ,diene, 1-3 butadiene, 1-2 butadiene,isoprene, 'p'iperylene and a small percentage but appreciable amount ofacetylenic hydrocarbons such as acetylene, methylacetylene,

ethyl acetylene, vinyl acetylene, etc. 7

Although such mixtures may be'distilled'to obtain lffractions consistingfor the most part of hydrocarbons having the same number of atoms inthe'mole'cule and the olefin content of each fraction may beconcentrated by the usual purification procedures such as by solventextraction, the acetylenic hydrocarbons and other highly unsaturatedimpurities of close to the same boiling point as the olefins anddiolefins tend to accompany the latter "during such treatments. Thus,for example, 1-3 butadiene which has been recovered from cracked oil gasby such treatment usually retains a minor amount of less f'than 0.1molecular equivalent of acetylenic hydrocarbon *such as methylacetylene, ethyl acetylene, etc. i and may also contain a small butappreciableproportion of un- "conjugated diolefins such as propadiene.

i Heretofore' it was practiced-to remove such highly unsaturatedimpurities by a process which involved the hydrogenation thereof over asuitable catalyst which was selective to the extent that negligibleamounts of 'olefins were destroyed. In such processes it was necessarythat the gas mixture contain 2% or less of unsaturated C hydrocarbons inorder to prevent fouling of'the catalyst. Further if the gas streamcontained dilute concentrations {of butadiene, the butadiene washydrogenated by passage over the catalyst and was effectively lost.Since butardiene is worth currently about14 to '15 cents per. pound,.itwould become desirable to effect its separation-from the raw gaspriorlto the hydrogenation stagein order-to ,prevent loss. thereof. Inaddition, 'as-indicated. abovegit the'total (3 unsaturate concentrationexceeded about 2%, "the. practice has been to effect separation from,the main body of gas prior to the hydrogenation step. In any event, theC olefins, if separated prior r tothe hydro- ,genation step, arecontaminated with acetylenic and diolefinic' impurities and requirefurtherjtreatinent in many fiiistances to be suitable fortheirintendeduse.

" It is an object. of the invention to provide" a simple and inexpensivemethod whereby vapor mixtures compris- 1 Eatented Oct. 3, 195.1

ice

ing a substantial proportion of unsaturated C hydrocarbon impuritiesincident to the manufacture of said olefins and a minor amount of highlyunsaturated acetylenes or alpha beta diolefins whereby the latterhighly'unsaturated'impurities may be catalytically hydrogenated withoutdestruction of'the unsaturated C hydrocarbons or the short chainolefins. A more specific object isjto provide a method of purifying byhydrogenationafnd thereafter by separation of unsaturated C 'olefinsanddi- 'olefins from a gas stream containing shorter chain olefins as amajor constituent. .Still another object involves hydrogenation of a gasstream containing C andjshorter chain olefins, separation of the Colefins therefrom and subsequent hydrogenation of the shorter chainolefins to effect" maximum purification thereof. Aside from theacetylenes, the highly unsaturated hydrocarbon impurities are in mostinstances alpha beta unsaturated aliphatic hydrocarbons having nohydrogen atom on the beta carbon atom. That is to say, they are alphaacetylenes or 1-2 diolefins. For convenience such impurities arereferred to herein as highly unsaturated hydrocarbon impurities. Otherobjects will be apparent from the following description of thisinvention.

"We have found that, by treatment of such gas compositions over aselective hydrogenation catalyst under conditions of temperature,pressure and space velocity such that the highly unsaturated impuritiesare removed to a level of from to 1000' parts per million, there issubstantially no loss of the, C conjugated diolefins; and 'olefins.Thereafter in one embodiment the C hydrocarbons are separated from thetreated gas mixture and the olefins, after concentration as bydistillation or solvent extraction, are passed over a palladium catalystso that the residual highly unsaturated impurities are substantiallycompletely removed. By this process, the need for a debutanizingoperation prior to the first hydrogenation stage is eliminated, theseparated C olefins and diolefins are purified to the extent thateificient utilization thereof is possible and the product olefinscontain only a tow parts per million of highly unsaturated impurities.

While We do not wish to be bound in any way by the accuracy of anytheoi'y' or hypothesis herein expressed, it is believed that thephenomenon of selectivity of acetylenes and alpha beta diolefins versusconjugated diolefins isnot primarily a matter of rate of reaction butrather is a matter of adsorption of the reactants on the activatedsurface of the catalyst. It is well known that the rate of hydrogenationreactions is accelerated by an increase in the hydrogenpartial'pressure. Our experience hasindicated, however, that thedifiference in the rate'of reaction between the various acetylenic anddiolefinic compounds is so marginal that selectivity between, forexample, an alpha beta diolefin and a'conjugated diolefin can not besatisfactorily explained. We proposed, however,jthat in addition totherfacto'rs already indicated selectivity is affected by the'adsorptionoffisayan acetylene on the most active centers of the catalysts surface.As a consequence the conjugated'diolefins are notad- "sorbed ontheactive surfaces in sufiicient quantities to effect appreciablehydrogenation thereof. Thus, by regplating the concentration of theacetylenes at the outlet "ofithelreactor' at a predetermined level,selectivitycan'be "achieved. In further expanding the theory ofthismechanism, our observations indicate that on the activated catalyticsurface the reactants are adsorbed in the following order: acetylene,alkyl acetylenes, alpha beta diolefins, conjugated diolefins and monoolefins. It follows, thereforep-that by adjusting the flow of reactantsover the catalystfso that there is maintained a level of the'first threeclasses of reactantsin the 'efliuent, the latter' twoj'ol'assesof"'reactants are'not hydrogenated. Furtherfwe have found that'if theconjugated diolefins are not'appreciably four carbon mono olefins have adefinite effect on this selectivity. It is believed, therefore, that thethree and four carbon mono olefins in some unexplained manner aifect ormask the adsorption of the conjugated butadiene without affecting theadsorption of the alpha beta diolefins. diene in a gas stream containingno three and four carbon mono olefins an acetylene conversion of between85 to 92% was obtained. However, with a gas stream containing about Cmono olefins an acetylene conversion of about 98% was achieved withoutnoticeable hydrogenation of bu-tadiene.

The invention will be better understood by referring to the accompanyingdrawing and the following examples.

FIGURE 1 is a diagrammatic fiowsheet of a conventional olefinpurification scheme. FIGURE 2 illustrates a preferred scheme forpurifying olefins according to this invention. I

Referring now to FiGURE 1, numeral 1 illustrates the source of the rawgas which may be received at a temperature of about 85 to about 110 F.and a pressure of about atmospheric. This gas comprises olefinscontaminated with acetylenic compounds, diolefinic compounds andcontains water vapor and entrained water as well as other undesirablecontaminants such as fine carbon particles, heavy hydrocarbons,aromatics, tars, etc. This gas mixture is passed through line 2 to thearomatic distillate removal operation designated by numeral 3 which isaccomplished by means of a scrubber wherein the gas is scrubbed toremove undesirable contaminants and thereby prevent deposition thereofon the catalyst within the hydrogenation reactor. The scrubbing mediummay comprise a heavy mineral oil such as a number 2 fuel oil which ispassed through the scrubber countercurrently to the movement of thecracked gas mixture. The heavy hydrocarbons as well as fine carbonparticles pass out the bottom of the scrubber through line 4 and thelight hydro- Thus, in order to prevent hydrogenation of butacarbons passthrough line 5 to the compression stage in-' dicated by numeral 6. Thegaseous mixture is then compressed to a pressure which may vary fromabout atmospheric to about 900 p.s.i.g., preferably, however, between 40and 600 p.s.i.g. The temperature of the gaseous mixture as a result ofthe compression is raised to a temperature of about 200 to 300 F. andthen passes through line 7 to the debutanizer designated by numeral 8.The mixture is scrubbed with a solvent, such as a light mineral oil,which has the property of selectively absorbing unsaturatedC, and higherhydrocarbons. The C s absorbed in oil are eliminated from the systemthrough line 9 and the C and lower hydrocarbons pass through line 10 tothe hydrogenation zone 11. Alternately the C hydrocarbons may be removedin the debutanizer zone 8 in several other ways. For example, thepyrolysis mixtore may be cooled and treated with a condensationcatalyst, such as aqueous sulfuric acid of activity sufiicient topolymerize and condense the diolefins without appreciably affecting theother unsaturated compounds present or the mixture may be cooled underpressure and therel to 60 atmospheres whereby the highly unsaturatedcompounds are selectively hydrogenated without appreciable hydrogenationof the mono olefins. This results in a gas containing highly unsaturatedhydrocarbons such as acetylenes in a concentration of about 10 to partsper million and a total loss of olefins of less than almost 2%. Suitablehydrogenation catalysts comprise the sulfides of nickel, cobalt andmolybdenum supported on inert carriers as well as compounds or mixturesof the metals and metal oxides of group 6 and 3 metals such ascobaltmolybdenum, nickel-chromium, nickel-molybdenum, etc. supported ondurable inert carriers. The treated gases 'are transferred via line 12to the acid gas removal stage designated by numeral 13. Acid gas such ascarbon dioxide and hydrogen sulfide is removed by scrubbing with causticor amines. The efiluent is carried via line 14 to the drying section 15wherein the gas is dried by passing over conventional desiccants as forexample activated alumina, activated bauxite, Porocel, etc. The driedgas is then conveyed vialine 16 to the low temperature absorptionsection which is designated by numeral 17. Normally liquid pentane isused as an absorbentyhowever, liquid propane or a mixture of liquidpentane and propane may be utilized. in this section the C and higherhydrocarbons areabsorbed in the liquid pentane mixture and hydrogen andmethane are passed overhead via line 18. The absorbent containing the Cand higher hydrocarbons are conveyed via line 19 to the strippingsection designated by numeral 20. In this section the absorbents areheated and the C s passed overhead While the C s and higher pass out thebottom with the liquid pentane through line 21. The C hydrocarbons passvia line 22 to a fractionator designated by numeral 23 wherein theresidual methane and hydrogen are separated from the C hydrocarbons. Theconcentrated olefins pass via line 24 to a tractionating columndesignated by numeral 25 which effects the final separation of the Colefins from the C paraifins. The concentrated olefins are then removedvia line 26 to storage. The ethylene thus concentrated to more than 99+%contains less than about 20 to 50 ppm. of acetylenes and other highlyunsaturated impurities.

Referring now to FIGURE 2, numeral 1 illustrates the source of the rawgas which may be received at a tem' perature of about to about F. and apressure of about atmospheric. This gas comprises olefins contaminatedwith acetylenic compounds, diolefins, and contains water vapor andentrained water as well as other undesirable contaminants such as .finecarbon particles, heavy hydrocarbons, aromatics, tars, etc. This gas ispassed through line 2 to the aromatic distillate removal operationdesignated by numeral 3 which is effected by means of an oil scrubberwherein the gas is scrubbed to remove undesirable contaminants. Thescrubbing medium may comprise a heavy mineral oil such as a number 2fuel oil which is passed through the scrubber countercurrently to themovement of the cracked gas mixture. These contaminants pass out thebottom of the scrubber; The light hydrocarbons pass through'line 5 to acompression stage indicated by numeral 6. The gaseous mixture is thencompressed to a pressure which may vary from 1 to 60 atmospheres.Preferably, however, the pressure is between about 40 and 600 -p.s.i.g.The temperature of the gaseous mixture as a result of the compression israised to a temperature of about 200 to 300 F. and then passes throughline 7 to the hydrogenation zone designated by numeral8. Thehydrogenation reactorcontains a bed of selective hydrogenation catalystsuch as the sulfides or oxides of group 8 metals as well as compounds ormixtures of metals or metal oxides of group 6 and group 8. Thus, forexample, suitable catalysts comprise the oxides of cobalt andmolybdenum, nickel and chromium, nickel and molybdenum, cobalt sulfide,nickel sulfide or molybdenum sulfide preferably on durable inertcarriers. The treated gas mixture is passed through the bed of selectivehydrogenation catalyst at a temperature in the'range of from about 200to about 600 F., a space velocity of about 500 to about 3000 and apressure of about from 1 to about 60 atmospheres. These conditions arevaried so :15 'that conversion of the highlyunsaturated compoundsis-such that the levelinthe 'efiiuent varies between about 100 and 1000p.p.m. If the initial gases contain a substantial proportion of carbonylsulfide compounds, the treated gases may bepassed over a bed of organicsulfur conversioncatalyst as is disclosed and claimed in our copendingap'plicatiomSerial No. 766,7l3, whichwas filed concurrently herewith,now US. Patent 2,959,627. A preferred catalyst which is disclosed inthat patent comprises a'mixture of copper'and chromium oxides supportedon'alumina. In this. manner the organic sulfur compoundsare'converted-to hydrogen sulfide Without ap- "pree'iablehydrogen'ationof the olefins and conjugated diolefins' and the gas ispassed via line-9 to the acid gas removal stage designatedby numeral 10.Acid gas, such "as-carbon dioxide-and hydrogen sulfide," is removed byscrubbing with caustic or amines. The efiluent is carried via line 11"tothe drying se'ction'12 where the gas'is dried by passing overconventional desiccantsas, for example, activated alumina, activatedbauxitefPoro'celyetc. The dried gas is then conveyed via line 13 to thelow temperature absorption section which is designated by numeral 14.Normally liquid pentane is used as an absorbent; however, liquidpropaneor amixture of liquid pentane and propane may be'utilized. In'thissection the'C and higher hydrocarbons are absorbed in the liquid pentanemixture and most of the hydrogen and methane'pass overhead via line 15.'Theabsorbent containing the C and higher hydrocarbons pass via line'16to'the stripping v --section 'designated'by'numeral 17. In thissectionthe absorbent-is heated and the C hydrocarbons are passedoverhead while the' C and higher hydrocarbons pass out the bottom withthe liquid pentane through line 18. "The C and'higher' hydrocarbonswhich include the purified 'butenes andbutadienemay be stripped'from theabsorbent'andrecovered. The C hydrocarbons pass 'via line 19 cc a"fractionator designated by numeral 20 where the residual methane andhydrogen are separated from the C hydrocarbons. The concentrated olefinspass via line 21 to afractionating column designated by numeral 22 whicheffects the final separation of the C olefins from the C parafiins.Someof theconcentrated olefins may then be of sufficient purity for'manyuses such as the production of ethylene oxide'and a portion of thismaterial may then be led 01f. forsuch purposes. However, the materialrequiring further purification isthen passed via line 23 to :ahydrogenation reactor designated by numeral 24. This reactor contains apalladium catalyst. supported on alumine .or silicagel in aconcentration. of from .Olto 0.1% and effects the final hydrogenation ofthe unsaturated impurities at a temperature in the range of 100 to 250F. with as little as 3 mols of hydrogen per mol of unsaturated impurity.By increasing the temperature any residual hydrogen may be consumed inthis process if desired. The ethylene thus concentrated to more than 99%contains less than about to p.p.m. of acetylenes or other highlyunsaturated impurities.

It will be noted that by use of this process the debutanizing operationprior to the initial hydrogenation is completely eliminated. The Colefins and diolefins are preserved and purified from highly unsaturatedimpurities and optionally from organic sulfur compounds. These materialsmay be separated from the stripping solution designated by numeral 18 ina form suitable for further use. Also by reason of the milderhydrogenation conditions in the initial hydrogenation zone, less overallolefin loss is encountered and in many cases a net gain of olefins(aside from the recovered butylene and butadiene) is obtained. Inaddition, it will be noted that by reason of the final purification ofthe material over a palladium catalyst the concentration of theimpurities in the product olefins is in a range of from 5 to 10 p.p.m.as compared to to 50 p.p.m. by conventional processes. The advantages ofoperating'in accordance with our invention can be fur-ther illustrated:byreferring- :to the f ollowin'g examples Example 1 V V A catalystscontaining on the final basis:

2.9% nickel sulfide T? 0.53% cobalt sulfide -0'.07% chromium sulfidepretreated bypassing hydrogen through the reactor'at a temperature of.750 to i800 f. F. for about 3 hours. "Thereafter a raw. gas:of thefollowing composition'was passed :throu'ghthe reactor at a pressure of.350 p.s.i.g.,ltemperature of 4509. 13. andv a space velocity of2000."Thefg'as mixture was as, follows:

'At these conditions" essentially no ethylene was hydrogenated. butapproximati'ely",70% of the butadiene was destrayed. 'L'Theacetylenejjnlthe"outlet gas was determined -10. be. about.j12.jp2p.m..LOr. a conversionlof acetylene lot over 98%. iiByloweringfthe'temperature to- 420F; and increasing the space velocity of 2700,there'was: no loss of. butadiene butjtheacetylene concentrationjin theoutlet wasabouf 5.180 ppm. .or an acetylene conversion of about 92%.

Example 2 -A i commercialicatalystr containing, about 20% cobalt'molybdateon a emediumsurface area support was tested under-identicalconditions and' with the identical, gasgmixture. It'was found thatata'ternperature of: 450 F.-.-and a space-velocityof 2000 about 50% ofthe butadienewas destroyed and aboutz220 p.p.m. of the acetylene. leakedin :the:;efliuent; gas. This amounted to an;acetylene*conversion of;about 97%. I By lowering the temperature-Etc .420":F.:--='and.iincreasing-:the spacevelocityi to 2700- no butadiene wasdestroyed and the acetylene concentration in the efiiuent increased toabout 1200 to 1500 p.p.m. amounting to an acetylene conversion of about81%. By lowering the space velocity to about 2500 the acetylene leakagewas reduced to about 900 p.p.m. with no appreciable hydrogenation ofeither butadiene or ethylene. This amounted to an acetylene conversionof about 87%.

It will be noted that the two catalysts are not exactly equivalent inactivity but that by varying the temperature and space velocity a goodconversion of acetylene can be achieved with no hydrogenation of thedesirable butadiene.

Example 3 A catalyst prepared identically with that of Example 1 wastested in an identical reactor at a pressure of p.s.i.g., a temperatureof 510 F. and a space velocity of 1000 utilizing a gas mixture of thefollowing composition:

Remainder Example 4 Utilizing the cobalt molybdate catalyst of Examplelunder the same conditions and with the same gas mixture as tested inExample 3, there was no loss of eitherethylene or butadiene and theacetylene in the effluent was in the range of 90 to 110 p.p.m. or anacetylene conversion of about 98%. Raising the temperature to 550 F.about 20% of the butadiene was hydrogenated and the acetyleneconcentration was about 40p.p.m.

It will be noted that in Examples 3 and'4 the gas mixture containedabout butadiene and over 11% of butylene or-a total concentration ofunsaturated C hydrocarbons of about In these examples it was possible toobtain a 98% conversion of acetylenes with little or no hydrogenation ofbutadiene, butylene. or ethylene.

' However, in Examples 1 and 2 (containing only a quarter of one percentof unsaturated C.{s),.a conversion of only 87 to 92% was obtainedwithouticoncomitant hydrogenation of the butadiene. It is felt that thecompetition of the C olefins for the active sites of the catalyst whichwere unoccupied by the acetylene increased the overall selectivity ofthe catalyst as to the butadiene. Therefore, even though more butadienewas contained in the gas streams of Examples 3 and Aascompared. to

Examples 1 and 2, less butadienewas hydrogenated with a specifiedacetylene conversion. Of course the effects of the partial pressure ofhydrogen and sulfurous compounds as well as flow rate and temperaturecan not and have not been overlooked. Nevertheless all other factorsremaining equal, the selectivity of the catalyst is increased as thepartial pressure of C olefins is increased.

It will be obvious to those skilled in the art that a novel process forthe purification and segregation ofolefins has been described whichshould not be limited in scope except as detailed in the appendedclaims.

We claim:

1. A process for the purification of desired constituents in an impuregas stream obtained by the pyrolysis of hydrocarbons, said streamcontaining C -C5 conjugated diolefins, ethylenes and C -C mono-olefinsas the desired constituents and highly unsaturated impurities includingacetylenes and alpha beta unsaturated hydrocarboshaving no hydrogen atomon the beta carbon atom as the constituents to be removed, comprisingthe steps of hydrogenating said impure gas stream with hydrogen at atemperatureof'about 200 F. to about 600 F., a space velocity of about500-3000 and a pressure of about 1 to atmospheres in the presence of ahydrogenation catalyst selected from thegroup consisting of oxides andsulfides' of cobalt, nickel, molybdenum, chromium, the foregoing metals,mixtures of said metals and mixtures of said sulfides and oxides whileregulating the concentration of acetylenes in said impure gas stream toprovide a level of from about to about 1000 parts of said acetylenes permillion parts of the gas stream at the outlet of the.

hydrogenation path whereby said acetylenes are selective 1y adsorbed onactive centers of said catalyst at said level of acetylene concentrationto effectively exclude adsorp tion and hydrogenation at said catalyst ofconjugated diolefins, ethylene and C -C mono-olefins, physicallyseparating said mixture into a first fraction containing ethylene andresidual acetylene and into a second fraction free from acetylenecontaining conjugated diolefins and C -C mono-olefins, hydrogenatingsaid first fraction in a second hydrogenation step with palladiumcatalyst at .100-400 F. to reduce said unsaturated impurities to a levelof less than 10 parts per million in said first fraction.

2. A process as defined inclaim l in which the gas stream contains about5% butadiene and about 11% of butylene and the concentration ofacetylene in the treated gas composition is maintained in the range ofabout 8 0 to 110 parts per million.

3. A process as defined in claim 1 in which the gas stream containsabout /1% up to 10% butadiene and the concentration of acetyleneat theoutlet of the treated gas composition in the first hydrogenation ismaintained at a level in excess of about parts per million but notgreater than 1000 parts per million.

4. A process as defined in claim l in which the gas from the firsthydrogenation step is passed with an excess of hydrogen over saidpalladium catalyst, the palladium thereof being present in aconcentration of from 0.01 to 0.1% on an inert support and said secondhydrogenation being carried out at a temperature of from 100 to 400 F.to remove the unsaturated impurities to a level of about 0-10 parts permillion.

References Cited in the file of this patent UNITED STATES PATENTS V jAnderson et al. Oct. 20, 1959

1. A PROCESS FOR THE PURIFICATION OF DESIRED CONSTITUENTS IN AN IMPUREGAS STREAM OBTAINED BY THE PYROLYSIS OF HYDROCARBONS, SAID STREAMCONTAINING C4-C5 CONJUGATED DIOLEFINS, ETHYLENES AND C3-C5 MONO-OLEFINSAS THE DESIRED CONSTITUENTS AND HIGHLY UNSATURATED IMPURITIES INCLUDINGACETYLENES AND ALPHA BETA UNSATURATED HYDROCARBONS HAVING NO HYDROGENATOM ON THE BETA CARBON ATOM AS THE CONSTITUENTS TO BE REMOVED,COMPRISING THE STEPS OF HYDROGENATING SAID IMPURE GAS STREAM WITHHYDROGEN AT A TEMPERATURE OF ABOUT 200*F. TO ABOUT 600*F., A SPACEVELOCITY OF ABOUT 500-3000 AND A PRESSURE OF ABOUT 1 TO 60 ATMOSPHERESIN THE PRESENCE OF A HYDROGENATION CATALYST SELECTED FROM THE GROUPCONSISTING OF OXIDES AND SULFIDES OF COBALT, NICKEL, MOLYBDENUM,CHROMIUM, THE FOREGOING METALS, MIXTURES OF SAID METALS AND MIXTURES OFSAID SULFIDES AND OXIDES WHILE REGULATING THE CONCENTRATION OFACETYLENES IN SAID IMPURE GAS STREAM AT THE OUTLET OF THE OF FROM ABOUT80 TO ABOUT 1000 PARTS OF SAID ACETYLENES PER MILLION PARTS OF THE GASSTREAM AT THE OUTLET OF THE HYDROGENATION PATH WHEREBY SAID ACETYLENESARE SELECTIVELY ADSORBED ON ACTIVE CENTERS OF SAID CATALYST AT SAIDLEVEL OF ACETYLENE CONCENTRATION TO EFFECTIVELY EXCLUDE ADSORPTION ANDHYDROGENATION AT SAID CATALYST OF CONJUGATED DIOLEFINS, ETHYLENE ANDC3-C5 MONO-OLEFINS, PHYSICALLY SEPARATING SAID MIXTURE INTO A FIRSTFRACTION CONTAINING ETHYLENE AND RESIDUAL ACETYLENE AND INTO A SECONDFRACTION FREE FROM ACETYLENE CONTAINING CONJUGATED DIOLEFINS AND C3-C5MONO-OLEFINS, HYDROGENATING SAID FIRST FRACTION IN A SECONDHYDROGENATION STEP WITH PALLADIUM CATALYST AT 100-400*F. TO REDUCE SAIDUNSATURATED IMPURITIES TO A